Niobium powder for capacitor, sintered body using the powder and capacitor using the same

ABSTRACT

An object of the present invention is to provide an antimony-containing niobium sintered body for a capacitor having a small specific leakage current value, an antimony-containing niobium powder for use in the sintered body, and a capacitor using the sintered body. In the present invention, an antimony-containing niobium powder having an antimony content of preferably about 0.1 to about 10 mol % and an average particle size of preferably about 0.2 to about 5 μm is used. By using this antimony-containing niobium powder, a sintered body and a capacitor are constructed.

CROSS REFERENCE TO RELATED APPLICATIONS

This is a continuation of application No. 09/842,627 filed Apr. 27,2003, now U.S. Pat. No. 6,643,120, which claims benefit pursuant to 35U.S.C. §119(e)(1) of the filing date of Provisional Application60/232,433 filed Sep. 14, 2000 pursuant to 35 U.S.C. §111(b); thedisclosures of which are incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to a niobium powder for capacitors, havinga large capacitance per unit mass and good specific leakage currentproperties. The present invention also relates to a sintered body usingthe powder and a capacitor using the sintered body.

BACKGROUND OF THE INVENTION

There is a demand for capacitors for use in electronic instruments, suchas portable telephones and personal computers, to have a small size anda large capacitance. Among these capacitors, a tantalum capacitor ispreferred because of its large capacitance for its size and goodperformance. In the tantalum capacitor, a sintered body of tantalumpowder is generally used for the anode moiety. In order to increase thecapacitance of the tantalum capacitor, it is necessary to increase themass of the sintered body or to use a sintered body with an increasedthe surface area by pulverizing the tantalum powder.

The method of increasing the mass of the sintered body unavoidablycauses enlargement of the capacitor shape, and thus, cannot satisfy therequirement for downsizing. On the other hand, in the method ofpulverizing tantalum powder to increase the surface area, the pore sizeof the tantalum sintered body decreases or closed pores increase at thestage of sintering. Therefore, impregnation of a cathode agent in alater process becomes difficult. As means for solving these problems, acapacitor using a sintered body of powder of a material having adielectric constant larger than that of tantalum is being studied.Materials having a larger dielectric constant include niobium andtitanium.

However, the sintered body produced from these materials is notsatisfactory because of its large “specific leakage current value”.Elemental niobium or titanium has a large dielectric constant, andtherefore, a capacitor having a large capacitance may be obtained.However, a small “specific leakage current value” is a key point forobtaining a capacitor having good reliability. By evaluating the leakagecurrent value per capacitance, namely, “specific leakage current value”,it can be estimated whether a large capacitance can be obtained in astate where leakage current value is reduced to a practically usablevalue or less.

The “specific leakage current value” as used herein is defined as avalue obtained when a dielectric layer is formed on the surface of asintered body by electrolytic oxidation, and a leakage current valuewhen a voltage corresponding to 70% of the chemical forming voltage iscontinuously applied at room temperature for 3 minutes is divided by theproduct of the chemical forming voltage during electrolytic oxidationand the capacitance. That is,Specific leakage current value=(LC/(C×V))(LC: leakage current value, C: capacitance, and V: forming voltage).

In the case of a sintered body using a tantalum powder, the specificleakage current value obtained from the capacitance and the leakagecurrent value described in the catalogue “CAPACITOR GRADE TANTALUM” ofShowa Cabot Super Metal is 1,500 pA/(μF·V) or less. In general, themeasured specific leakage current value for guaranteeing this specificleakage current value is said to be from ⅓ to ¼ of the value in thecatalogue and is preferably 400 pA/(μF·V) or less.

However, in conventional sintered body capacitors where a niobium powderusing elemental niobium or a titanium powder is used, the specificleakage current value is large and exceeds the above-described value.Accordingly, these capacitors are lacking in reliability as a capacitorand are not used in practice.

JP-A-55-157226 (the term “JP-A” as used herein means an “unexaminedpublished Japanese patent application”) discloses a method for producinga sintered element for capacitors, where agglomerated powder is moldedunder pressure into a niobium fine powder having a particle size of 2.0μm or less, the fine powder is sintered, the molded and sintered body iscut into fine pieces, a lead part is joined thereto, and then thesepieces are again sintered. However, this patent publication disclosesneither a niobium powder containing antimony nor properties of thecapacitor manufactured using this powder.

U.S. Pat. No. 4,084,965 discloses a capacitor manufactured using aniobium powder of 5.1 μm obtained by hydrogenating a niobium ingot andpulverizing it. However, U.S. Pat. No. 4,084,965 discloses neither aniobium powder containing antimony nor properties of the capacitormanufactured using this powder.

JP-A-10-242004 discloses a technique of partially nitriding niobium,thereby improving the leakage current value. However, JP-A-10-242004discloses neither a niobium powder containing antimony nor properties ofthe capacitor manufactured using this powder.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a niobium powder forcapacitors, which can yield a capacitor having a large capacitance perunit mass and good specific leakage current properties; a sintered bodyusing the powder; and a capacitor using the sintered body.

As a result of extensive investigations, the present inventors haveaccomplished the present invention, which comprises the followingembodiments.

(1) A niobium powder for capacitors, comprising niobium and antimony.

(2) The niobium powder for capacitors as described in 1 above, whereinthe content of antimony is from about 0.1 to about 10 mol %.

(3) The niobium powder for capacitors as described in 1 or 2 above,wherein the average particle size of the powder is from about 0.2 μm toless than about 5 μm.

(4) The niobium powder for capacitors as described in any one of 1 to 3above, wherein the niobium powder comprises at least one member selectedfrom the group consisting of niobium nitride, niobium carbide, niobiumboride and niobium sulfide.

(5) A sintered body using the niobium powder described in any one of 1to 4 above.

(6) The sintered body as described in 5 above, which has a specificleakage current value of about 400 pA/(μF·V) or less.

(7) A capacitor comprising the sintered body described in 6 above as oneelectrode, a dielectric material formed on the surface thereof, and asecond electrode.

(8) The capacitor as described in 7 above, wherein the dielectricmaterial comprises niobium oxide.

(9) The capacitor as described in 8 above, wherein the niobium oxide isformed by electrolytic oxidation.

(10) The capacitor as described in 7 above, wherein the second electrodeis at least one material (compound) selected from an electrolyticsolution, an organic semiconductor and an inorganic semiconductor.

(11) The capacitor as described in 7 above, wherein the another partelectrode is formed of an organic semiconductor and the organicsemiconductor is at least one organic semiconductor selected from thegroup consisting of an organic semiconductor comprising a benzopyrrolinetetramer and chloranile, an organic semiconductor mainly comprisingtetrathiotetracene, an organic semiconductor mainly comprisingtetracyanoquinodimethane, and an organic semiconductor mainly comprisingan electrically conducting polymer obtained by doping a dopant into apolymer comprising two or more repeating units represented by formula(1) or (2):

wherein R¹ to R⁴, which may be the same or different, each representshydrogen, an alkyl group having from 1 to 6 carbon atoms or an alkoxygroup having from 1 to 6 carbon atoms, X represents an oxygen atom, asulfur atom or a nitrogen atom, R⁵ is present only when X is a nitrogenatom and represents hydrogen or an alkyl group having from 1 to 6 carbonatoms, and R¹ and R², or R³ and R⁴ may be combined with each other toform a ring.

(12) The capacitor as described in 10 above, wherein the organicsemiconductor is at least one member selected from polypyrrole,polythiophene and substitution derivatives thereof.

DESCRIPTION OF THE PRESENT INVENTION

In the present invention, the capacitance of a capacitor is generallyrepresented by the following formula:Capacitance C=∈×(S/d)(C: capacitance, ∈: dielectric constant, S: specific surface area, andd: distance between electrodes).

Here, d=k×V (k: constant, V: forming voltage), therefore, C=∈×(S/(k×V))and then C×V=(∈/k)×S. When the specific leakage current value is definedas (LC/(C×V)) (LC: leakage current value), the following formula isestablished:

Specific leakage current value:=(LC/(C×V))=(LC/((∈/k(×S))

From this formula, it is considered that the specific leakage currentvalue can be reduced by any one method selected from a method ofreducing LC, a method of increasing (C×V), a method of increasing ∈ anda method of increasing S.

In the present invention, the antimony-containing niobium powder for usein the production of a sintered body is preferably specified to have anaverage particle size of less than about 5 μm, so that the specificsurface area of the powder can be increased. As a result, a large CVvalue and in turn, a small specific leakage current value can beattained.

However, if the average particle size of the antimony-containing niobiumpowder is less than 0.2 μm, impregnation of a cathode agent becomesdifficult as described above when a sintered body is produced from thepowder, and as a result, the fabricated capacitor cannot have a largecapacitance. Based on these reasons, the average particle size of theantimony-containing niobium powder of the present invention ispreferably specified to a value of about 0.2 μm to less than about 5 μmand in this range, the specific leakage current value can be made small.

Niobium is known to have a dielectric constant (∈) as large as about twotimes the dielectric constant of tantalum. However, whether or notantimony is a valve metal was not known and accordingly, whether or not∈ increases by incorporating antimony into niobium was not known priorto the present invention

In addition, niobium has a high bonding strength to an oxygen elementcompared with tantalum, and therefore, oxygen in the electrolytic oxidefilm is liable to diffuse toward the internal niobium metal side. On theother hand, in a sintered body of the present invention, a part ofniobium is bonded to antimony and therefore, it is presumed that oxygenin the electrolytic oxide film is not easily bonded to the internalniobium metal and is inhibited from diffusing toward the metal side. Asa result, the stability of the electrolytic oxide film can be maintainedand the effect of reducing the LC can be obtained.

The sintered body obtained by the present invention exhibits a goodspecific leakage current value, as described above, and a preferredvalue of about 400 pA/(μF·V) or less. In the present invention, thespecific leakage current value can be further reduced to about 300pA/(μF·V) or less by using a preferred antimony content and averageparticle size of the antimony-containing niobium powder.

One embodiment of the present invention for obtaining the sintered bodyof the present invention is described below. The antimony content in theantimony-containing niobium powder used for producing a sintered body isan important feature of the present invention. If the antimony contentis too small, the oxygen in the electrolytic oxide film cannot beinhibited from diffusing toward the internal niobium metal side, and asa result, the stability of the electrolytic oxide film cannot bemaintained and the effect of reducing LC cannot be obtained. If theantimony content is excessively large, the niobium content in theantimony-containing niobium powder is reduced and the capacitancedecreases. Accordingly, the amount of antimony in theantimony-containing niobium powder is preferably from about 0.1 to about10 mol %, and from the viewpoint of further reducing the specificleakage current value, more preferably from about 0.3 to about 3 mol %.

The antimony-containing niobium powder for use in the production of asintered body preferably has an average particle size of about 0.2 μm toless than about 5 μm. If the average particle size is less than about0.2 μm, when a sintered body is produced from the powder and a capacitoris fabricated using the sintered body, the pores inside the sinteredbody are excessively small. Therefore, a cathode material, which isdescribed later, cannot be easily impregnated. If the average particlesize is about 5 μm or more, a preferred specific leakage current canhardly be obtained, because the capacitance and the leakage currentdiffer in variation with respect to the average particle size.Accordingly, the average particle size is preferably from about 0.2 μmto less than about 5 μm and from the viewpoint of further reducing thespecific leakage current value, more preferably from about 0.5 μm toless than about 2 μm.

The average particle size as used in the present invention means a D₅₀value (a particle size when the cumulative % by mass is 50% by mass)measured using a particle size distribution measuring apparatus(“Micro-track”, trade name). The antimony-containing niobium powderhaving an average particle size in the above-described range can beobtained, for example, by a method of pulverizing and dehydrogenating ahydride of a niobium-antimony alloy ingot, pellet or powder, or by amethod of carbon-reducing a mixture of niobium oxide and antimony oxide.In the case of obtaining the antimony-containing niobium powder bypulverizing and dehydrogenating a hydride of a niobium-antimony alloyingot, an antimony-containing niobium powder having a desired averageparticle size can be obtained by controlling the amount of theniobium-antimony alloy ingot hydrogenated, the pulverization time, thegrinding machine or the like.

The thus-obtained antimony-containing niobium powder may be mixed with aniobium powder having an average particle size of about 0.2 μm to lessthan about 5 μm. The niobium powder added here may be obtained, forexample, by a method of pulverizing a sodium reduction product ofpotassium fluoroniobate, a method of pulverizing and dehydrogenating ahydroxide of a niobium ingot, or a method of carbon-reducing a niobiumoxide.

In order to further improve the leakage current value of thethus-obtained antimony-containing niobium powder, a part of theantimony-containing niobium powder may be bonded to at least one ofnitrogen, carbon, boron and sulfur. The powder may comprise any of thesebonded products with nitrogen, carbon, boron or sulfur, namely,antimony-containing niobium nitride, antimony-containing niobiumcarbide, antimony-containing niobium boride and antimony-containingniobium sulfide. Also, these bonded products may be used in combinationof two, three or four thereof.

The sum total of the bond amounts, that is, the contents of nitrogen,carbon, boron and sulfur, varies depending on the shape of theantimony-containing niobium powder. However, in the case of powderhaving an average particle size of from about 0.2 to about 5 μm, the sumtotal is preferably from about 50 to about 200,000 ppm, more preferablyfrom about 200 to about 20,000 ppm. If the total content is less thanabout 50 ppm, the LC property cannot be improved, whereas if it exceedsabout 200,000 ppm, the capacitance property deteriorates and thefabricated product is not suitable as a capacitor.

The nitriding of the antimony-containing niobium powder can be performedby any one of liquid nitriding, ionitriding, gas nitriding or by acombination thereof. Among these, the method of performing the gasnitriding of niobium powder in a nitrogen gas atmosphere is preferredbecause the apparatus used is simple and operation is easy. For example,gas nitriding can be attained by allowing the above-describedantimony-containing niobium powder to stand in a nitrogen gasatmosphere.

The antimony-containing niobium powder having a desired nitrided amountcan be obtained by performing the nitriding treatment at an atmospheretemperature of about 2,000° C. or less for a period of tens of hours.The treatment time can be shortened by performing this treatment at ahigher temperature.

The carbonization of the antimony-containing niobium powder may beperformed by any one of gas carbonization, solid phase carbonization andliquid carbonization. For example, the antimony-containing niobiumpowder may be carbonized by allowing it to stand with a carbon sourcesuch as carbon material or an organic material having carbon (e.g.,methane), at about 2,000° C. or less for several minutes to tens ofhours under reduced pressure.

The boronizing of the antimony-containing niobium powder may beperformed by any one of gas boronizing and solid phase boronizing. Forexample, the antimony-containing niobium powder may be boronized byallowing it to stand with a boron source, such as boron pellet or boronhalide (e.g., trifluoroboron), at about 2,000° C. or less for severalminutes to tens of hours under reduced pressure.

The sulfurization of the antimony-containing niobium powder may beperformed by any one of gas sulfurization, ion sulfurization and solidphase sulfurization. For example, the gas sulfurization in a sulfur gasatmosphere can be attained by allowing the antimony-containing niobiumpowder to be present in a sulfur gas atmosphere. The antimony-containingniobium powder having a desired sulfurized amount can be obtained byperforming the sulfurization treatment in an atmosphere at a temperatureof about 2,000° C. or less for a period of tens of hours. By performingthis treatment at a higher temperature, the treatment time can beshortened.

The antimony-containing niobium powder for capacitors of the presentinvention may be used after granulating the antimony-containing niobiumpowder into an appropriate shape or may be used by mixing an appropriateamount of non-granulated niobium powder after the granulation. Forgranulation, a conventionally known method can be used. Examples thereofinclude a method where non-granulated antimony-containing niobium powderis allowed to stand in a high vacuum, heated to a predeterminedtemperature and then cracked, and a method where non-granulatedantimony-containing niobium powder is mixed with a binder, such ascamphor, poly(acrylic acid) or poly(methyl acrylic acid ester), and thencracked.

The antimony-containing niobium sintered body of the present inventionis produced by sintering the above-described antimony-containing niobiumpowder. One example of the method for producing the sintered body isdescribed below, however, the production method for the sintered body ofthe present invention is not limited thereto. For example, theantimony-containing niobium powder may be press-molded into apredetermined shape and then heated at a temperature of about 500 toabout 2,000° C., preferably from about 900 to about 1,500° C., morepreferably from about 900 to about 1,250° C., for several minutes toseveral hours under a pressure of about 1 to about 10⁻⁷ Torr ((1 to10⁻⁷)×133 Pa).

The manufacture of a capacitor device is described below.

For example, a lead wire comprising a valve-acting metal such as niobiumor tantalum and having appropriate shape and length is prepared and thislead wire is integrally molded during the above-described press-moldingof the niobium powder so that a part of the lead wire is inserted intothe inside of the molded article, thereby the lead wire can work out toa leading line of the sintered body.

Using this sintered body as an electrode of a pair of electrodes, acapacitor can be manufactured by interposing a dielectric materialbetween this electrode and another electrode. The dielectric materialused here for the capacitor is preferably a dielectric material mainlycomprising niobium oxide. The dielectric material mainly comprisingniobium oxide can be easily obtained, for example, by chemically formingthe antimony-containing niobium sintered body as an electrode in anelectrolytic solution. The chemical forming of the antimony-containingniobium electrode in an electrolytic solution is usually performed usingan aqueous protonic acid solution such as aqueous 0.1% phosphoric acidsolution, sulfuric acid, 10% acetic acid or adipic acid. In the case ofchemically forming the antimony-containing niobium electrode in anelectrolytic solution to obtain a niobium oxide dielectric material, thecapacitor of the present invention is an electrolytic capacitor and theantimony-containing niobium electrode serves as an anode.

The other electrode of the capacitor of the present invention is notparticularly limited and for example, at least one material (compound)selected from electrolytic solutions, organic semiconductors andinorganic semiconductors known in the art of aluminum electrolyticcapacitors, may be used. Specific examples of the electrolytic solutioninclude a dimethylformamide-ethylene glycol mixed solution havingdissolved therein 5% by mass of an isobutyltripropylammoniumborotetrafluoride electrolyte, and a propylene carbonate-ethylene glycolmixed solution having dissolved therein 7% by mass of tetraethylammoniumborotetrafluoride.

Specific examples of the organic semiconductor include an organicsemiconductor comprising a benzene-pyrroline tetramer and chloranile, anorganic semiconductor mainly comprising tetrathiotetracene, an organicsemiconductor mainly comprising tetracyanoquinodimethane, and an organicsemiconductor mainly comprising an electrically conducting polymerobtained by doping a dopant into a polymer comprising two or morerepeating units represented by formula (1) or (2):

wherein R¹ to R⁴, which may be the same or different, each representshydrogen, an alkyl group having from 1 to 6 carbon atoms or an alkoxygroup having from 1 to 6 carbon atoms, X represents an oxygen atom, asulfur atom or a nitrogen atom, R⁵ is present only when X is a nitrogenatom and represents hydrogen or an alkyl group having from 1 to 6 carbonatoms, and R¹ and R², or R³ and R⁴ may be combined with each other toform a ring. For the dopant, any known dopant can be used without limit.

Specific examples of the inorganic semiconductor include an inorganicsemiconductor mainly comprising lead dioxide or manganese dioxide, andan inorganic semiconductor comprising triiron tetraoxide. Thesesemiconductors may be used individually or in combination of two or morethereof.

In the specification, “mainly comprising” recited above means to becomprising about 50 mass % and more, preferably about 80 mass % andmore.

Examples of the polymer containing two or more repeating unitsrepresented by formula (1) or (2) include polyaniline, polyoxyphenylene,poly(phenylene sulfide), polythiophene, polyfuran, polypyrrole,polymethylpyrrole, and substitution derivatives and copolymers thereof.Among these, preferred are polypyrrole, polythiophene and substitutionderivatives thereof (e.g., poly(3,4-ethylene-dioxothiophene)).

In the case where the organic or inorganic semiconductor used has anelectrical conductivity of 10⁻² to 10³ S·cm⁻¹, the fabricated capacitorcan have a smaller impedance value and the capacitance can be furtherincreased at a high frequency.

Furthermore, when the other electrode is solid, an electrical conductinglayer may be provided thereon to attain good electrical contact with anexterior leading line (for example, lead frame).

The electrical conducting layer can be formed, for example, by thesolidification of an electrically conducting paste, plating,metallization or formation of a heat-resistant electrically conductingresin film. Preferred examples of the electrically conducting pasteinclude silver paste, copper paste, aluminum paste, carbon paste andnickel paste, and these may be used individually or in combination oftwo or more thereof. When using two or more kinds of pastes are used,the pastes may be mixed or may be superposed one on the other asseparate layers. The electrically conducting paste applied is thensolidified by allowing it to stand in air or under heating. Examples ofthe plating include nickel plating, copper plating, silver plating andaluminum plating. Examples of the metal deposited include aluminum,nickel, copper and silver.

More specifically, for example, aluminum paste and silver paste arestacked in this order on the second electrode and are molded with amaterial such as epoxy resin, thereby constructing a capacitor. Thiscapacitor may have a tantalum lead which is sintered and moldedintegrally with the niobium sintered body or welded afterward.

The thus-constructed capacitor of the present invention is jacketedusing, for example, resin mold, resin case, metallic jacket case,dipping of resin or laminate film, and then used as a capacitor productfor various uses.

When the other electrode is liquid, the capacitor constructed by theabove-described electrodes and dielectric material is housed, forexample, in a can electrically connected to the other electrode to forma capacitor. In this case, the electrode side of the antimony-containingniobium sintered body is guided outside through a niobium or tantalumlead, described above, and at the same time, insulated from the canusing an insulating rubber or the like.

By producing a sintered body using niobium powder according to thepresent invention, as described above, and fabricating a capacitor fromthe sintered body, a capacitor having good reliability can be obtained.

EXAMPLES

The present invention is described in detail below by referring to theExamples, however, the present invention is not limited to theseExamples. Unless indicated otherwise herein, all parts, percents, ratiosand the like are by weight.

In the following Examples, the capacitance and the leakage current ofthe sintered body are measured as follows.

Measurement of Capacitance of Sintered Body

A capacitance at 120 Hz measured at room temperature by connecting anLCR measuring device of HP (LCR Meter manufactured by Hewlett-Packard)between a sintered body dipped in 30% sulfuric acid and an electrode oftantalum material placed in a sulfuric acid solution was designated asthe capacitance of the sintered body.

Measurement of Leakage Current of Sintered Body

A d.c. voltage corresponding to 70% of the chemical forming voltage atthe time of forming a dielectric material was continuously appliedbetween a sintered body dipped in an aqueous 20% phosphoric acidsolution and an electrode placed in an aqueous phosphoric acid solution,at room temperature for 3 minutes, and thereafter a current value wasmeasured and designated as the leakage current value (LC value) of thesintered body. In the present invention, a voltage of −14 V was applied.

In the following Examples, the capacitance and the leakage current valueof the capacitor worked into a chip were measured as follows.

Capacitance of Capacitor

The capacitance at 120 Hz was measured at room temperature by connectingan LCR measuring apparatus of HP between the terminals of themanufactured chip and designated as the capacitance of the capacitorworked into a chip.

Leakage Current of Capacitor

Among rated voltages (e.g., 2.5 V, 4 V, 6.3 V, 10 V, 16 V, 25 V, etc.),a d.c. voltage close to about ⅓ to about ¼ of the chemical formingvoltage at the time of forming a dielectric material was continuouslyapplied at room temperature between the terminals of the manufacturedchip for 1 minute and thereafter, a current value was measured anddesignated as the leakage current value of the capacitor worked into achip. In the present invention, a voltage of 6.3 V was applied.

Example 1

Using 98.6 g of niobium ingot and 1.4 g of antimony powder, anantimony-containing niobium ingot having an antimony content of 1.1 mol% was produced by arc melting. In an SUS 304-made reactor, 50 g of theobtained ingot was placed, and hydrogen was continuously introducedthereinto at 400° C. for 10 hours. After cooling, the hydrogenatedantimony-containing niobium lump was placed in an SUS 304-made potcontaining SUS-made balls and pulverized for 10 hours. Subsequently,this hydride was formed into a 20 vol % slurry with water, chargedtogether with zirconia balls into an SUS 304-made wet grinding machine(“Attritor”, trade name), and wet pulverized for 7 hours. The resultingslurry was centrifuged and decanted to obtain a pulverized product.

The pulverized product was dried in a vacuum under conditions of 1 Torr(133 Pa) and 50° C. Subsequently, the hydrogenated antimony-containingniobium powder was dehydrogenated under heating at 10⁻⁴ Torr (133×10⁻⁴Pa) and 400° C. for 1 hour. The produced antimony-containing niobiumpowder had an average particle size of 1.3 μm and the antimony contentmeasured by the atomic absorption analysis was 1 mol %. Thethus-obtained antimony-containing niobium powder was molded togetherwith a 0.3-mmφ (“φ” means diameter) in niobium wire to produce a moldedarticle having a size of approximately 0.3×0.18×0.45 cm (about 0.1 g).

This molded article was allowed to stand in a vacuum of 3×10⁻⁵ Torr at1,200° C. for 30 minutes and a sintered body was obtained. The sinteredbody obtained was electrochemically formed in an aqueous 0.1% phosphoricacid solution at a temperature of 80° C. for 200 minutes by applying avoltage of 20 V to form a dielectric layer on the surface. Thereafter,the capacitance in 30% sulfuric acid and the leakage current(hereinafter simply referred to as “LC”) in an aqueous 20% phosphoricacid solution were measured. The results obtained are shown in Table 1.

Examples 2 to 6-1

In order to change the antimony content of the antimony-containingniobium powder, antimony-containing niobium ingots having an antimonycontent of 0.1 to 15 mol % were produced while varying the amounts ofniobium and antimony treated by arc melting. Thereafter, using 50 g ofthe antimony-containing niobium ingot having an antimony concentrationas shown in Table 1, a sintered body was produced by the same operationas in Example 1, and the capacitance and the LC value of each sinteredbody were measured. The results obtained are shown in Table 1.

Comparative Example 1, Examples 6-2 and 6-3

Antimony-containing niobium ingots having an antimony content of 0 mol%, 0.04 mol % or 19.3 mol % were produced. Thereafter, using 50 g of theantimony-containing niobium ingot having an antimony concentration of 0mol %, 0.04 mol % and 19.3 mol %, a sintered body was produced by thesame operation as in Examples 2 to 6, and the capacitance and the LCvalue of each sintered body were measured. The results obtained areshown in Table 1.

Examples 7 to 11-1

In order to change the average particle size of antimony-containingniobium powder, a hydrogenated antimony-containing niobium lump havingan antimony content of 1.2 mol % was produced in the same manner as inExample 1, placed in an SUS 304-made pot containing iron-made balls andpulverized for 10 hours. Thereafter, 50 g of this hydride was formedinto a 20% slurry with water, charged together with zirconia balls intoan SUS 304-made wet grinding machine (“Attritor”, trade name), and wetpulverized by varying the time. The resulting slurry was centrifuged anddecanted to obtain a pulverized product. The pulverized product obtainedwas dried in a vacuum under the conditions of 1 Torr and 50° C.

Subsequently, the hydrogenated antimony-containing niobium powder wasdehydrogenated under heating at 10⁻⁴ Torr and 400° C. for 1 hour toobtain antimony-containing niobium powder. The obtainedantimony-containing niobium powder had an average particle size of 0.2to 5.1 μm. Furthermore, the thus-obtained antimony-containing niobiumpowder was molded together with a 0.3-mmφ niobium wire to produce amolded article having a size of approximately 0.3 cm×0.18 cm×0.45 cm(about 0.1 g).

Each of these molded articles was allowed to stand in a vacuum of 2×10⁻⁵Torr (2×10⁻⁵×133 Pa) at 1,200° C. for 30 minutes to obtain a sinteredbody. The capacitance and the LC value of each sintered body obtainedwere measured in the same manner as in Example 1. The results are shownin Table 2.

Examples 11-2 and 11-3

Hydrogenated antimony-containing niobium powder having an antimonycontent of 1.2 mol % was treated by the same operation as in Examples 7to 11-1 to obtain antimony-containing niobium powder having an antimonycontent of 1.2 mol % and an average particle size of 8.8 μm or 22 μm. Byusing each of the antimony-containing niobium powder obtained, asintered body was produced and the content and LC value thereof weremeasured. The results obtained are shown in Table 2.

Examples 12 to 15

In order to change the sintering temperature of the antimony-containingniobium sintered body, an antimony-containing niobium powder having anantimony content of 1.1 mol % and an average particle size of 1.2 μm wasproduced in the same manner as in Example 1 and molded together with a0.3-mmφ niobium wire to produce a molded article having a size ofapproximately 0.3×0.18×0.45 cm (about 0.1 g). Then, the molded articlewas allowed to stand in a vacuum of 6×10⁻⁶ to 5×10⁻⁵ Torr at atemperature of 1,100 to 1,300° C. for 30 to 100 minutes to obtainvarious sintered bodies. The capacitance and the LC value of eachsintered body obtained were measured in the same manner as in Example 1.The results are shown in Table 3.

Examples 16 to 20

In order to obtain an antimony-containing niobium nitride, 10 g ofantimony-containing niobium powder having an antimony content of 1.2 mol% and an average particle size of 1.4 μm was produced in the same manneras in Example 1 and charged into an SUS 304-made reactor, and nitrogenwas continuously introduced thereinto at 300° C. for 0.5 to 20 hours toobtain antimony-containing niobium nitrides. The nitrogen amount of eachnitride was determined using a nitrogen amount measuring apparatusmanufactured by LECO, which determines the nitrogen amount from thermalconductivity. The ratio of the measured value to the separately measuredmass of powder was designated as the nitrided amount. The nitridedamount was from 0.02 to 0.88% by mass. The thus-obtainedantimony-containing niobium nitride was molded and sintered in the samemanner as in Example 1, and the sintered body obtained waselectrochemically formed in an aqueous 0.1% phosphoric acid solution ata temperature of 80° C. for 200 minutes by applying a voltage of 20 V toform a dielectric layer on the surface. Thereafter, the capacitance in30% sulfuric acid and the LC value in an aqueous 20% phosphoric acidsolution were measured. The results obtained are shown in Table 4.

TABLE 1 Average Specific Antimony Particle LC Leakage Content SizeCapacitance Value Current Value [mol %] [μm] [μF] [μA] [pA/(μF · V)]Example 1 1.1 1.3 502 2.8 279 Example 2 0.09 1.3 487 3.8 390 Example 30.45 1.4 495 2.9 297 Example 4 3.8 1.3 488 3.0 307 Example 5 9.7 1.2 4733.0 317 Example 6-1 14.3 1.2 449 3.0 334 Comparative 0 1.3 432 39.1 4525Example 1 Example 6-2 0.04 1.3 451 7.8 865 Example 6-3 19.3 1.1 402 3.3410

TABLE 2 Average Specific Antimony Particle LC Leakage Content SizeCapacitance Value Current Value [mol %] [μm] [μF] [μA] [pA/(μF · V)]Example 7 1.2 0.2 1167 9.3 399 Example 8 1.2 0.7 649 4.4 342 Example 91.2 1.3 502 3.0 299 Example 10 1.2 2.6 268 1.7 317 Example 1.2 5.1 2021.3 322 11-1 Example 1.2 12 91 0.8 440 11-2 Example 1.2 22 62 0.6 48411-3

TABLE 3 Specific Sintering Leaking Temper- Sintering Capacitance LCValue Current Value ature [° C.] Time [min] [μF] [μA] [pA/(μF · V)]Example 12 1100 100 689 4.4 319 Example 13 1150 100 601 3.7 308 Example14 1200 30 510 3.0 299 Example 15 1300 30 302 1.7 281

TABLE 4 Nitro- Specific Antimony gen LC Leakage Content ContentCapacitance Value Current Value [mol %] [wt %] [μF] [μA] [pA/(μF · V)]Example 16 1.2 0.02 499 2.7 270 Example 17 1.2 0.12 505 2.9 287 Example18 1.2 0.26 503 2.8 278 Example 19 1.2 0.45 497 3.1 312 Example 20 1.20.88 501 3.5 349

Examples 21 to 24

In order to obtain a sintered body comprising a mixture ofantimony-containing niobium powder and niobium powder,antimony-containing niobium powder having an antimony content of 10 mol% and an average particle size of 2.4 μm was obtained in the same manneras in Example 1. Separately, into a nickel-made crucible, 20 g ofpotassium fluoroniobate thoroughly dried in a vacuum at 80° C. andsodium in a molar amount of 10 times the potassium fluoroniobate werecharged and allowed to perform a reduction reaction at 1,000° C. for 20hours in an argon atmosphere. After the completion of reaction, thereduction product was cooled, washed with water, washed with 95%sulfuric acid and then with water in sequence, dried in a vacuum andpulverized for 40 hours using a ball mill in an alumina pot containingsilica alumina balls. The pulverized product was dipped and stirred in a3:2 (by mass) mixed solution of 50% nitric acid and 10% aqueous hydrogenperoxide.

Thereafter, the pulverized product was thoroughly washed with wateruntil the pH reached 7 to remove impurities, and dried in a vacuum. Theproduced niobium powder had an average particle size of 2.6 μm. Thethus-obtained antimony-containing niobium powder was well mixed withniobium powder at an arbitrary ratio, as shown in Table 5, the mixturewas molded and sintered in the same manner as in Example 1 to obtainsintered bodies. The capacitance and the LC value of each sintered bodywere measured and the results obtained are shown in Table 5.

Examples 25 to 28

In order to obtain a sintered body of antimony-containing niobiumnitride comprising a mixture of antimony-containing niobium powder andniobium powder, antimony-containing niobium powder having an antimonycontent of 10 mol % and an average particle size of 1.2 μm was obtainedin the same manner as in Example 1. Separately, 50 g of niobium ingotwas placed in an SUS 304-made reactor and hydrogen was continuouslyintroduced thereinto at 400° C. for 12 hours. After cooling, thehydrogenated niobium lump was placed in an SUS 304-made pot containingiron-made balls and pulverized for 10 hours. This pulverized product wascharged into the above-described SUS 304-made reactor and againhydrogenated under the above-described conditions.

Subsequently, this hydride was formed into a 20 vol % slurry with water,charged together with zirconia balls into an SUS 304-made wet grindingmachine (“Attritor”, trade name), and wet pulverized for 6 hours. Theresulting slurry was centrifuged and decanted to obtain a pulverizedproduct. The pulverized product was dried in a vacuum under theconditions of 1 Torr and 50° C. Subsequently, the hydrogenated niobiumpowder was dehydrogenated under heating at 10⁻⁴ Torr and 400° C. for 1hour. The produced niobium powder had an average particle size of 1.3μm. The thus-obtained antimony-containing niobium powder was well mixedwith niobium powder at an arbitrary ratio, as shown in Table 6, nitrideswere obtained in the same manner as in Example 16 to 20, and molded andsintered to obtain sintered bodies. The capacitance and the LC value ofeach sintered body were measured and the results obtained are shown inTable 6.

TABLE 5 Mixing Ratio (antimony- Specific containing niobium Capaci- LCLeakage powder/niobium tance Value Current Value powder by reduction)[μF] [μA] [pA/(μF · V)] Example 21 90:10 239 1.7 356 Example 22 50:50261 1.9 364 Example 23 20:80 259 1.6 309 Example 24 10:90 268 1.7 317

TABLE 6 Mixing Ratio (antimony- containing Specific niobium powder/Nitrogen LC Leakage niobium powder Content Capacit- Value Current Valueby pulverization) [wt %] ance [μF] [μA] [pA/(μF · V)] Example 25 90:100.05 469 3.0 320 Example 26 50:50 0.51 486 2.9 298 Example 27 20:80 0.95495 2.9 292 Example 28 10:90 0.25 505 3.0 297

Examples 29 to 35

50 Units of each sintered body were obtained, in Example 29 in the samemanner as in Example 1, in Example 30 in the same manner as in Example5, in Example 31 in the same manner as in Example 7, in Example 32 inthe same manner as in Example 13, in Example 33 in the same manner as inExample 18, in Example 34 in the same manner as in Example 23, and inExample 35 in the same manner as in Example 28. Each of these sinteredbodies was electrochemically formed using an aqueous 0.1% phosphoricacid solution at a voltage of 20 V for 200 minutes to form an oxidedielectric film on the surface. Subsequently, an operation of dippingeach sintered body in an aqueous 60% manganese nitrate solution andheating it at 220° C. for 30 minutes was repeated to form a manganesedioxide layer as the other electrode layer on the oxide dielectric film.On this other electrode layer, a carbon layer and a silver paste layerwere stacked in this order. After mounting a lead frame thereon, thedevice as a whole was molded with an epoxy resin to manufacture achip-type capacitor. The capacitance and the LC value each in average ofthe chip-type capacitors (n=50 units in each Example) are shown in Table7. The LC value is a value measured at room temperature by applying avoltage of 6.3 V for 1 minute.

TABLE 7 Sintered Body Chip Specific Leakage Current LC Value Value[pA/(μF · V)] [μA] Capacitance [μF] Example 29 279 2.6 467 Example 30317 2.7 445 Example 31 399 8.2 1080 Example 32 308 3.3 555 Example 33278 2.6 469 Example 34 309 1.5 252 Example 35 297 2.9 472

Examples 36 to 42

50 Units of each sintered body were obtained, in Example 36 in the samemanner as in Example 2, in Example 37 in the same manner as in Example6-1, in Example 38 in the same manner as in Example 8, in Example 39 inthe same manner as in Example 15, in Example 40 in the same manner as inExample 19, in Example 41 in the same manner as in Example 21, and inExample 42 in the same manner as in Example 26. Each of these sinteredbodies was electrochemically formed using an aqueous 0.1% phosphoricacid solution at a voltage of 20 V for 200 minutes to form an oxidedielectric film on the surface. Subsequently, an operation of dippingeach sintered body in a mixed solution of an aqueous 35% lead acetatesolution and an aqueous 35% ammonium persulfate solution (1:1 by volume)and allowing the reaction to proceed at 40° C. for 1 hour was repeatedto form a mixed layer of lead dioxide and lead sulfate as the otherelectrode layer on the oxide dielectric film. On this other electrodelayer, a carbon layer and a silver paste layer were stacked in thisorder. After mounting a lead frame thereon, the device as a whole wasmolded with an epoxy resin to manufacture a chip-type capacitor. Thecapacitance and the LC value each in average of the chip-type capacitors(n=50 units in each Example) are shown in Table 8. The LC value is avalue measured at room temperature by applying a voltage of 6.3 V for 1minute.

TABLE 8 Sintered Body Chip Specific Leakage Current LC Value Value[pA/(μF · V)] [μA] Capacitance [μF] Example 36 390 2.5 452 Example 37334 2.6 421 Example 38 342 4.7 599 Example 39 281 1.8 289 Example 40 3122.6 462 Example 41 356 1.4 229 Example 42 298 2.6 455

The sintered body using the antimony-containing niobium powder of thepresent invention exhibits good properties in the specific leakagecurrent value, and the capacitor manufactured using the sintered body isfavored with a small LC value, and therefore, a highly reliablecapacitor can be obtained.

While the invention has been described in detail and with reference tospecific embodiments thereof, it will be apparent to one skilled in theart that various changes and modifications can be made therein withoutdeparting from the spirit and scope thereof.

1. A niobium powder for capacitors, comprising niobium and antimony. 2.The niobium powder for capacitors as claimed in claim 1, wherein acontent of antimony is from about 0.1 to about 10 mol %.
 3. The niobiumpowder for capacitors as claimed in claim 1, wherein an average particlesize of the powder is from about 0.2 μm to less than about 5 μm.
 4. Theniobium powder for capacitors as claimed in claim 2, wherein an averageparticle size of the powder is from about 0.2 μm to less than about 5μm.
 5. A sintered body comprising sintered niobium powder, wherein theniobium powder is described in claim
 1. 6. A sintered body comprisingsintered niobium powder, wherein the niobium powder is described inclaim
 2. 7. The sintered body as claimed in claim 5, which has aspecific leakage current value of about 400 pA/(μF·V) or less.
 8. Thesintered body as claimed in claim 6, which has a specific leakagecurrent value of about 400 pA/(μF·V) or less.
 9. A capacitor comprisingthe sintered body described in claim 7, as one electrode, a dielectricmaterial formed on the surface thereof, and a second electrode.
 10. Acapacitor comprising the sintered body described in claim 8, as oneelectrode, a dielectric material formed on the surface thereof, and asecond electrode.
 11. The capacitor as claimed in claim 9, wherein thedielectric material comprises niobium oxide.
 12. The capacitor asclaimed in claim 10, wherein the dielectric material comprises niobiumoxide.
 13. The capacitor as claimed in claim 11, wherein the niobiumoxide is formed by electrolytic oxidation.
 14. The capacitor as claimedin claim 12, wherein the niobium oxide is formed by electrolyticoxidation.
 15. The capacitor as claimed in claim 9, wherein the secondelectrode is at least one material selected from the group consisting ofan electrolytic solution, an organic semiconductor and an inorganicsemiconductor.
 16. The capacitor as claimed in claim 10, wherein thesecond electrode is at least one material selected from the groupconsisting of an electrolytic solution, an organic semiconductor and aninorganic semiconductor.
 17. The capacitor as claimed in claim 9,wherein the second electrode is at least one organic semiconductorselected from the group consisting of an organic semiconductorcomprising a benzopyrroline tetramer and chloranile, an organicsemiconductor mainly comprising tetrathiotetracene, an organicsemiconductor mainly comprising tetracyanoquinodimethane, and an organicsemiconductor mainly comprising an electrically conducting polymerobtained by doping a dopant into a polymer comprising two or morerepeating units represented by formula (1) or (2):

wherein R¹ to R⁴, which may be the same or different, each representshydrogen, an alkyl group having from 1 to 6 carbon atoms or an alkoxygroup having from 1 to 6 carbon atoms, X represents an oxygen atom, asulfur atom or a nitrogen atom, R⁵ is present only when X is a nitrogenatom and represents hydrogen or an alkyl group having from 1 to 6 carbonatoms, and R¹ and R², or R³ and R⁴ may be combined with each other toform a ring.
 18. The capacitor as claimed in claim 10, wherein thesecond electrode is at least one organic semiconductor selected from thegroup consisting of an organic semiconductor comprising a benzopyrrolinetetramer and chloranile, an organic semiconductor mainly comprisingtetrathiotetracene, an organic semiconductor mainly comprisingtetracyanoquinodimethane, and an organic semiconductor mainly comprisingan electrically conducting polymer obtained by doping a dopant into apolymer comprising two or more repeating units represented by formula(1) or (2):

wherein R¹ to R⁴, which may be the same or different, each representshydrogen, an alkyl group having from 1 to 6 carbon atoms or an alkoxygroup having from 1 to 6 carbon atoms, X represents an oxygen atom, asulfur atom or a nitrogen atom, R⁵ is present only when X is a nitrogenatom and represents hydrogen or an alkyl group having from 1 to 6 carbonatoms, and R¹ and R², or R³ and R⁴ may be combined with each other toform a ring.
 19. The capacitor as claimed in claim 15, wherein theorganic semiconductor is at least one member selected from the groupconsisting of polypyrrole, polythiophene and substitution derivativesthereof.
 20. The capacitor as claimed in claim 16, wherein the organicsemiconductor is at least one member selected from the group consistingof polypyrrole, polythiophene and substitution derivatives thereof.